This invention relates to a fluid purifier for removing a volatile contaminant from a fluid. More particularly but not exclusively, it relates to a fluid purifier for recovering chlorofluorocarbons from hydraulic fluids such as hydraulic oil used in ground and aerospace vehicles.
Certain chlorofluorocarbons (hereinafter referred to as CFC's) are widely used as solvents for cleaning machines on account of their excellent degreasing properties. Examples of such CFC's are Freon TF and 1,1,1-trichloroethane. When a machine is cleaned using a CFC-containing solvent, a thin film of the solvent adheres to the surface of the machine. When the machine is again used after it has been cleaned, the solvent film comes into contact and becomes mixed with oil (such as hydraulic fluid or lubricating oil) for the machine. Furthermore, at the time of cleaning, some of the solvent may drip into an oil sump of the machine and mix with oil in the sump. Therefore, whenever CFC's are used for cleaning a machine, oil in the machine is inevitably contaminated by the CFC's. Small amounts of a CFC-containing solvent in oil are not harmful, but over time, the concentration of the solvent gradually increases and the oil can become diluted to the point that it can no longer be employed and must be replaced.
It is not possible to dispose of oil contaminated with CFC's by burning it for heating purposes, since combustion of the oil releases CFC's into the atmosphere, with adverse effects on the ozone layer. Furthermore, although Freon TF is not particularly dangerous, when trichloroethane 1,1,1, is burned, it can form phosgene, which is highly toxic. In addition, hydraulic fluid for jets may become polluted not only with CFC's but also with jet fuel, which is explosive if improperly burned.
Therefore, at the present time, old hydraulic fluid and other types of oil contaminated with CFC's must be disposed of as a hazardous waste material at considerable expense. For this reason, there is a need for an apparatus which can efficiently remove CFC's from oil without releasing the CFC's to the atmosphere or generating harmful by-products.
It is possible to remove CFC's from oil by adsorption using carbon beds. However, adsorption beds have the drawback that they are too large to be easily transported. Furthermore, they have the problem that they must be regenerated. Regeneration is usually performed using low-pressure steam, which requires large amounts of energy to generate. Equipment must also be provided for condensing the steam and carrying out water separation after the bed is regenerated. Therefore, an adsorption bed is disadvantageous from the standpoints of both size and cost.
It is also possible to remove CFC's from oil using a degreasing still. However, degreasing stills are designed to separate oil from a mixture (such as a mixture of Freon and oil) in which oil is the minor component of the mixture, and they are inefficient for removing small amounts of CFC's from mixtures containing large quantities of oil. Since lubricating oil must be replaced when the concentration of CFC's in the oil is at most about 10%, degreasing stills are unsuitable for purifying such oil.